1. Field of the Invention
The present invention relates to compression ignition internal combustion engines including exhaust gas recirculation and variably operating between an exhaust gas recirculation (EGR) mode and a non-EGR mode, preferably known as boost mode, wherein an engine control monitors operating conditions and calculates a critical intake manifold temperature under operating conditions as a function of a selected set of influence factors to predict condensation, and when operating conditions would result in condensation in the intake manifold during EGR mode, operating the engine in the non-EGR mode.
2. Background Art
Condensation is a problem identified in engines using exhaust gas recirculation (EGR). The hot exhaust gas from diesel engines includes a mixture of water vapor from the burnt fuel and ambient air. EGR engines recirculate a limited amount of exhaust gas back into the intake manifold to combust any unused fuel and byproducts. Due to the lower temperature of the intake air at the intake manifold, condensation may occur in the manifold when exhaust gas is mixed with fresh air in the intake manifold. For a given operating condition (with fixed air/fuel ratio (AFR), the variable degree of recirculation (% EGR) and intake manifold pressure (IMP)) and for a given ambient conditions such as ambient temperature (ATI) and relative humidity (ATIRH), the water vapor will condense at a dew point temperature. The dew point temperature is defined as the intake manifold critical temperature (IMT_) and is influenced by many conditions. The condensate is acidic due to presence of compounds of nitrogen and sulfur from fuel. Moreover, the engine and the equipment in which it may be installed operate in wide ranges of ambient temperatures, for example, −25 deg C. to 50 deg C. and relative humidity 0% to 100%, for highway.
The use and variation of the EGR operation may be controlled if all of influences could be sensed concurrently. However, some of the influential conditions or parameters cannot be readily or economically sensed in the environment of equipment, particularly vehicles, in ambient conditions and modes of operation. For example, if RH cannot be measured, then a fixed relative humidity may be assumed depending on what kind of protection is required. For example, over protection may be desired by assuming a high humidity value, where EGR entry is limited to preserve the engine. Alternatively, under protection may assume a low humidity so that EGR entry is enhanced to reduce emissions, but at the risk of reduced engine life.